Differential effects of CB(1) neutral antagonists and inverse agonists on gastrointestinal motility in mice

Early life adversity promotes gastrointestinal dysfunction through a sex-dependent phenotypic switch in enteric glia

Irritable bowel syndrome and related disorders of gut-brain interaction (DGBI) are common and exhibit a complex, poorly understood etiology that manifests as abnormal gut motility and pain. Risk factors such as biological sex, stressors during critical periods, and inflammation are thought to influence DGBI vulnerability by reprogramming gut-brain circuits, but the specific cells affected are unclear. Here, we used a model of early life stress to understand cellular mechanisms in the gut that produce DGBIs. Our findings identify enteric glia as a key cellular substrate in which stress and biological sex converge to dictate DGBI susceptibility. Enteric glia exhibit sexual dimorphism in genes and functions related to cellular communication, inflammation, and disease susceptibility. Experiencing early life stress has sex-specific effects on enteric glia that cause a phenotypic switch in male glia toward a phenotype normally observed in females. This phenotypic transformation is followed by physiological changes in the gut, mirroring those observed in DGBI in humans. These effects are mediated, in part, by alterations to glial prostaglandin and endocannabinoid signaling. Together, these data identify enteric glia as a cellular integration site through which DGBI risk factors produce changes in gut physiology and suggest that manipulating glial signaling may represent an attractive target for sex-specific therapeutic strategies in DGBIs.

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Targeting the endocannabinoid system for the treatment of abdominal pain in irritable bowel syndrome

The management of visceral pain in patients with disorders of gut-brain interaction, notably irritable bowel syndrome, presents a considerable clinical challenge, with few available treatment options. Patients are increasingly using cannabis and cannabinoids to control abdominal pain. Cannabis acts on receptors of the endocannabinoid system, an endogenous system of lipid mediators that regulates gastrointestinal function and pain processing pathways in health and disease. The endocannabinoid system represents a logical molecular therapeutic target for the treatment of pain in irritable bowel syndrome. Here, we review the physiological and pathophysiological functions of the endocannabinoid system with a focus on the peripheral and central regulation of gastrointestinal function and visceral nociception. We address the use of cannabinoids in pain management, comparing them to other treatment modalities, including opioids and neuromodulators. Finally, we discuss emerging therapeutic candidates targeting the endocannabinoid system for the treatment of pain in irritable bowel syndrome.

Role of CB1 receptors in the acute regulation of small intestinal permeability: effects of high-fat diet

The endocannabinoid system of the gastrointestinal tract is involved in the control of intestinal barrier function. Whether the cannabinoid 1 (CB1) receptor is expressed on the intestinal epithelium and acutely regulates barrier function has not been determined. Here, we tested the hypothesis that ligands of the CB1 receptor acutely modulate small intestinal permeability and that this is associated with altered distribution of tight junction proteins. We examined the acute effects of CB1 receptor ligands on small intestinal permeability both in chow-fed and 2-wk high-fat diet (HFD)-fed mice using Ussing chambers. We assessed the distribution of CB1 receptor and tight junction proteins using immunofluorescence and the expression of CB1 receptor using PCR. A low level of CB1 expression was found on the intestinal epithelium. CB1 receptor was highly expressed on enteric nerves in the lamina propria. Neither the CB1/CB2 agonist CP55,940 nor the CB1 neutral antagonist AM6545 altered the flux of 4kDa FITC dextran (FD4) across the jejunum or ileum of chow-fed mice. Remarkably, both CP55,940 and AM6545 reduced FD4 flux across the jejunum and ileum in HFD-fed mice that have elevated baseline intestinal permeability. These effects were absent in CB1 knockout mice. CP55,940 reduced the expression of claudin-2, whereas AM6545 had little effect on claudin-2 expression. Neither ligand altered the expression of ZO-1. Our data suggest that CB1 receptor on the intestinal epithelium regulates tight junction protein expression and restores barrier function when it is increased following exposure to a HFD for 2 wk.NEW & NOTEWORTHY The endocannabinoid system of the gastrointestinal tract regulates homeostasis by acting as brake on motility and secretion. Here we show that when exposed to a high fat diet, intestinal permeability is increased and activation of the CB1 receptor on the intestinal epithelium restores barrier function. This work further highlights the role of the endocannabinoid system in regulating intestinal homeostasis when it is perturbed.

Inhibiting Fatty Acid Amide Hydrolase Ameliorates Enteropathy in Diabetic Mice: A Cannabinoid 1 Receptor Mediated Mechanism

Gastrointestinal (GI) dysmotility in diabetics exhibits fecal incontinence or constipation which affects patients’ quality of life. In this study, we aimed to understand the pattern of GI transit in type 1 diabetic (T1D) mice and whether inhibiting endocannabinoid degradation would exhibit therapeutic effect. Whole gut-transit time and fecal-pellet output were measured at 16 week post-diabetes. T1D mice treated with fatty acid amide hydrolase (FAAH) inhibitor URB597 showed reduced fecal output as well as improved gut transit time. Cannabinoid 1 receptor antagonist, AM251 blocked the effects of URB597, which may demonstrate that FAAH inhibitor is a potential remedial strategy for GI dysmotility.

The Cannabinoid Receptor Type 1 Positive Allosteric Modulator ZCZ011 Attenuates Naloxone-Precipitated Diarrhea and Weight Loss in Oxycodone-Dependent Mice

Opioid use disorder reflects a major public health crisis of morbidity and mortality in which opioid withdrawal often contributes to continued use. However, current medications that treat opioid withdrawal symptoms are limited by their abuse liability or lack of efficacy. Although cannabinoid 1 (CB₁) receptor agonists, including Δ⁹-tetrahydrocannabinol, ameliorate opioid withdrawal in both clinical and preclinical studies of opioid dependence, this strategy elicits cannabimimetic side effects as well as tolerance and dependence after repeated administration. Alternatively, CB₁ receptor positive allosteric modulators (PAMs) enhance CB₁ receptor signaling and show efficacy in rodent models of pain and cannabinoid dependence but lack cannabimimetic side effects. We hypothesize that the CB₁ receptor PAM ZCZ011 attenuates naloxone-precipitated withdrawal signs in opioid-dependent mice. Accordingly, male and female mice given an escalating dosing regimen of oxycodone, a widely prescribed opioid, and challenged with naloxone displayed withdrawal signs that included diarrhea, weight loss, jumping, paw flutters, and head shakes. ZCZ011 fully attenuated naloxone-precipitated withdrawal-induced diarrhea and weight loss and reduced paw flutters by approximately half, but its effects on head shakes were unreliable, and it did not affect jumping behavior. The antidiarrheal and anti-weight loss effects of ZCZ0111 were reversed by a CB₁ not a cannabinoid receptor type 2 receptor antagonist and were absent in CB₁ (-/-) mice, suggesting a necessary role of CB₁ receptors. Collectively, these results indicate that ZCZ011 completely blocked naloxone-precipitated diarrhea and weight loss in oxycodone-dependent mice and suggest that CB₁ receptor PAMs may offer a novel strategy to treat opioid dependence. SIGNIFICANCE STATEMENT: Opioid use disorder represents a serious public health crisis in which current medications used to treat withdrawal symptoms are limited by abuse liability and side effects. The CB₁ receptor positive allosteric modulator (PAM) ZCZ011, which lacks overt cannabimimetic behavioral effects, ameliorated naloxone-precipitated withdrawal signs through a CB₁ receptor mechanism of action in a mouse model of oxycodone dependence. These results suggest that CB₁ receptor PAMs may represent a viable strategy to treat opioid withdrawal.

Localisation of Cannabinoid and Cannabinoid-Related Receptors in the Horse Ileum

Colic is a common digestive disorder in horses and one of the most urgent problems in equine medicine. A growing body of literature has indicated that the activation of cannabinoid receptors could exert beneficial effects on gastrointestinal inflammation and visceral hypersensitivity. The localisation of cannabinoid and cannabinoid-related receptors in the intestine of the horse has not yet been investigated. The purpose of this study was to immunohistochemically localise the cellular distribution of canonical and putative cannabinoid receptors in the ileum of healthy horses. Distal ileum specimens were collected from six horses at the slaughterhouse. The tissues were fixed and processed to obtain cryosections which were used to investigate the immunoreactivity of canonical cannabinoid receptors 1 (CB1R) and 2 (CB2R), and three putative cannabinoid-related receptors: nuclear peroxisome proliferator-activated receptor-alpha (PPARα), transient receptor potential ankyrin 1 and serotonin 5-HT1a receptor (5-HT1aR). Cannabinoid and cannabinoid-related receptors showed a wide distribution in the ileum of the horse. The epithelial cells showed immunoreactivity for CB1R, CB2R and 5-HT1aR. Lamina propria inflammatory cells showed immunoreactivity for CB2R and 5-HT1aR. The enteric neurons showed immunoreactivity for CB1R, transient receptor potential ankyrin 1 and PPARα. The enteric glial cells showed immunoreactivity for CB1R and PPARα. The smooth muscle cells of the tunica muscularis and the blood vessels showed immunoreactivity for PPARα. The present study represents a histological basis which could support additional studies regarding the distribution of cannabinoid receptors during gastrointestinal inflammatory diseases as well as studies assessing the effects of non-psychotic cannabis-derived molecules in horses for the management of intestinal diseases.

Whole and Isolated Protein Fractions Differentially Affect Gastrointestinal Integrity Markers in C57Bl/6 Mice Fed Diets with a Moderate-Fat Content

Various proteins or protein fractions reportedly positively affect gastrointestinal integrity and inflammation in diets providing >45% energy as fat. This study tested whether benefits were seen in diets providing 30% of energy as fat. Purified diets (PD) with isolated soy protein (ISP), dried whole milk powder (DWMP), milk fat globule membrane (MFGM), or milk protein concentrate (MPC) as protein sources were fed to C57BL/6J mice (n = 15/diet group) for 13 weeks. MFGM-fed mice were heaviest (p < 0.005) but remained within breeder norms. Growth rates and gut motility were similar for all PD-fed mice. FITC-dextran assessed gut permeability was lowest in DWMP and MFGM (p = 0.054); overall, plasma endotoxin and unprovoked circulating cytokines indicated a non-inflammatory state for all PD-fed mice. Despite differences in cecal butyrate and intestinal gene expression, all PDs supported gastrointestinal health. Whole milk provided more positive effects compared to its fractions. However, ISP-fed mice showed a >370%, (p < 0.006) increase in colonic myeloperoxidase activity indicative of tissue neutrophil infiltration. Surprisingly, FITC-dextran and endotoxin outcomes were many folds better in PD-fed mice than mice (strain, vendor, age and sex matched) fed a “chow-type” nutritionally adequate non-PD. Additional variables within a diet’s matrix appear to affect routine indicators or gastrointestinal health.

Cannabinoid and Cannabinoid-Related Receptors in the Myenteric Plexus of the Porcine Ileum

An important piece of evidence has shown that molecules acting on cannabinoid receptors influence gastrointestinal motility and induce beneficial effects on gastrointestinal inflammation and visceral pain. The aim of this investigation was to immunohistochemically localize the distribution of canonical cannabinoid receptor type 1 (CB1R) and type 2 (CB2R) and the cannabinoid-related receptors transient potential vanilloid receptor 1 (TRPV1), transient potential ankyrin receptor 1 (TRPA1), and serotonin receptor 5-HT1a (5-HT1aR) in the myenteric plexus (MP) of pig ileum. CB1R, TRPV1, TRPA1, and 5-HT1aR were expressed, with different intensities in the cytoplasm of MP neurons. For each receptor, the proportions of the immunoreactive neurons were evaluated using the anti-HuC/HuD antibody. These receptors were also localized on nerve fibers (CB1R, TRPA1), smooth muscle cells of tunica muscularis (CB1R, 5-HT1aR), and endothelial cells of blood vessels (TRPV1, TRPA1, 5-HT1aR). The nerve varicosities were also found to be immunoreactive for both TRPV1 and 5-HT1aR. No immunoreactivity was documented for CB2R. Cannabinoid and cannabinoid-related receptors herein investigated showed a wide distribution in the enteric neurons and nerve fibers of the pig MP. These results could provide an anatomical basis for additional research, supporting the therapeutic use of cannabinoid receptor agonists in relieving motility disorders in porcine enteropathies.

Perturbed Mitochondrial Dynamics Is a Novel Feature of Colitis That Can Be Targeted to Lessen Disease

BACKGROUND & AIMS

Mitochondria exist in a constantly remodelling network, and excessive fragmentation can be pathophysiological. Mitochondrial dysfunction can accompany enteric inflammation, but any contribution of altered mitochondrial dynamics (ie, fission/fusion) to gut inflammation is unknown. We hypothesized that perturbed mitochondrial dynamics would contribute to colitis.

METHODS

Quantitative polymerase chain reaction for markers of mitochondrial fission and fusion was applied to tissue from dextran sodium sulfate (DSS)-treated mice. An inhibitor of mitochondrial fission, P110 (prevents dynamin related protein [Drp]-1 binding to mitochondrial fission 1 protein [Fis1]) was tested in the DSS and di-nitrobenzene sulfonic acid (DNBS) models of murine colitis, and the impact of DSS ± P110 on intestinal epithelial and macrophage mitochondria was assessed in vitro.

RESULTS

Analysis of colonic tissue from mice with DSS-colitis revealed increased mRNA for molecules associated with mitochondrial fission (ie, Drp1, Fis1) and fusion (optic atrophy factor 1) and increased phospho-Drp1 compared with control. Systemic delivery of P110 in prophylactic or treatment regimens reduced the severity of DSS- or DNBS-colitis and the subsequent hyperalgesia in DNBS-mice. Application of DSS to epithelial cells or macrophages caused mitochondrial fragmentation. DSS-evoked perturbation of epithelial cell energetics and mitochondrial fragmentation, but not cell death, were ameliorated by in vitro co-treatment with P110.

CONCLUSIONS

We speculate that the anti-colitic effect of systemic delivery of the anti-fission drug, P110, works at least partially by maintaining enterocyte and macrophage mitochondrial networks. Perturbed mitochondrial dynamics can be a feature of intestinal inflammation, the suppression of which is a potential novel therapeutic direction in inflammatory bowel disease.

Effects of O-1602 and CBD on TNBS-induced colonic disturbances

BACKGROUND

This study attempted to provide the effects and mechanisms of two cannabinoids, O-1602 and cannabidiol (CBD), on colonic motility of 2,4,6-trinitro-benzene sulfonic acid (TNBS) colitis.

METHODS

TNBS was used to induce the model of motility disorder. G protein-coupled receptor 55 (GPR55) expression was detected using real-time PCR and immunohistochemistry in colon. Pro-inflammatory cytokines and myeloperoxidase were also measured. The colonic motility was measured by upper GI transit in vivo and recorded using electrical stimulation organ bath technique in vitro. Freshly isolated smooth muscle from the rat colon were applied to determine the membrane potential and Ca²⁺ -ATPase activity, respectively.

KEY RESULTS

CBD or O-1602 separately improved inflammatory conditions significantly in TNBS-induced colitis rats. However, sole CBD pretreatment reduced GPR55 expression, which was up-regulated in TNBS colitis. O-1602 and CBD each lowered MPO and IL-6 levels remarkably in TNBS colitis, while TNF-α levels experienced no change. CBD rescued the downward colonic motility in TNBS colitis in vivo; however, it decreased the upward contraction of the smooth muscle strip under electrical stimulation in vitro. Pretreatment with CBD prevented against TNBS-induced changes of Ca²⁺ -ATPase activity of smooth muscle cells. However, membrane potential of the smooth muscle cells decreased by TNBS experienced no change after O-1602 or CBD import.

CONCLUSIONS & INFERENCES

The present study suggested that CBD participated in the regulation of colonic motility in rats, and the mechanisms may be involved in the regulation of inlammatory factors and Ca²⁺ -ATPase activity through GPR55.

Overcoming the Psychiatric Side Effects of the Cannabinoid CB1 Receptor Antagonists: Current Approaches for Therapeutics Development

The Cannabinoid CB1 Receptor (CB1R) is involved in a variety of physiological pathways and has long been considered a golden target for therapeutic manipulation. A large body of evidence in both animal and human studies suggests that CB1R antagonism is highly effective for the treatment of obesity, metabolic disorders and drug addiction. However, the first-in-class CB1R antagonist/inverse agonist, rimonabant, though demonstrating effectiveness for obesity treatment and smoking cessation, displays serious psychiatric side effects, including anxiety, depression and even suicidal ideation, resulting in its eventual withdrawal from the European market. Several strategies are currently being pursued to circumvent the mechanisms leading to these side effects by developing neutral antagonists, peripherally restricted ligands, and allosteric modulators. In this review, we describe the progress in the development of therapeutics targeting the CB1R in the last two decades.

Multiple endocannabinoid-mediated mechanisms in the regulation of energy homeostasis in brain and peripheral tissues

The endocannabinoid (eCB) system is widely expressed in many central and peripheral tissues, and is involved in a plethora of physiological processes. Among these, activity of the eCB system promotes energy intake and storage, which, however, under pathophysiological conditions, can favour the development of obesity and obesity-related disorders. It is proposed that eCB signalling is evolutionary beneficial for survival under periods of scarce food resources. Remarkably, eCB signalling is increased both in hunger and in overnutrition conditions, such as obesity and type-2 diabetes. This apparent paradox suggests a role of the eCB system both at initiation and at clinical endpoint of obesity. This review will focus on recent findings about the role of the eCB system controlling whole-body metabolism in mice that are genetically modified selectively in different cell types. The current data in fact support the notion that eCB signalling is not only engaged in the development but also in the maintenance of obesity, whereby specific cell types in central and peripheral tissues are key sites in regulating the entire body's energy homeostasis.

Cannabinoid CB1 receptor neutral antagonist AM4113 inhibits heroin self-administration without depressive side effects in rats

Cannabinoid CB₁ receptors (CB₁Rs) have been shown to be a promising target in medication development for the treatment of addiction. However, clinical trials with SR141716A (rimonabant, a selective CB₁R antagonist/inverse agonist) for the treatment of obesity and smoking cessation failed due to unwanted side effects, such as depression, anxiety, and suicidal tendencies. Recent preclinical studies suggest that the neutral CB₁R antagonist AM4113 may retain the therapeutic anti-addictive effects of SR141716A in nicotine self-administration models and possibly has fewer unwanted side effects. However, little is known about whether AM4113 is also effective for other drugs of abuse, such as opioids and psychostimulants, and whether it produces depressive side effects similar to SR141716A in experimental animals. In this study, we demonstrated that systemic administration of AM4113 (3 and 10 mg/kg) dose-dependently inhibited the self-administration of intravenous heroin but not cocaine or methamphetamine, whereas SR141716A (3 and 10 mg/kg) dose-dependently inhibited the self-administration of heroin and methamphetamine but not cocaine. In the electrical brain-stimulation reward (BSR) paradigm, SR141716A (3 and 10 mg/kg) dose-dependently increased the BSR stimulation threshold (i.e., decreased the stimulation reward), but AM4113 had no effect on BSR at the same doses, suggesting that SR141716A may produce aversive effects while AM4113 may not. Together, these findings show that neutral CB₁R antagonists such as AM4113 deserve further research as a new class of CB₁R-based medications for the treatment of opioid addiction without SR141716A-like aversive effects.

Endocannabinoid regulation of homeostatic feeding and stress-induced alterations in food intake in male rats

BACKGROUND AND PURPOSE

Stress is known to reduce food intake. Many aspects of the stress response and feeding are regulated by the endocannabinoid system, but the roles of anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in stress-induced anorexia are unclear.

EXPERIMENTAL APPROACH

Effects of acute restraint stress on endocannabinoids were investigated in male Sprague-Dawley rats. Systemic and central pharmacological inhibition of fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL) was used to assess the effects of elevated AEA and 2-AG on homeostatic feeding and on food consumption after stress. Animals were pretreated with the FAAH inhibitor, PF-04457845, or the MAGL inhibitor, MJN110, before 2 h acute restraint stress or 2 h homecage period without food.

KEY RESULTS

Restraint stress decreased hypothalamic and circulating AEA, with no effect in the gastrointestinal tract, while 2-AG content in the jejunum (but not duodenum) was reduced. PF-04457845 (30 μg), given i.c.v., attenuated stress-induced anorexia via CB₁ receptors, but reduced homeostatic feeding in unstressed animals through an unknown mechanism. On the other hand, systemic administration of MJN110 (10 mg·kg^-1 ) reduced feeding, regardless of stress or feeding status and inhibited basal intestinal transit in unstressed rats. The ability of MAGL inhibition to reduce feeding in combination with stress was independent of CB₁ receptor signalling in the gut as the peripherally restricted CB₁ receptor antagonist, AM6545 did not block this effect.

CONCLUSIONS AND IMPLICATIONS

Our data reveal diverse roles for 2-AG and AEA in homeostatic feeding and changes in energy intake following stress.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Novel derivatives of 1,2,3-triazole, cannabinoid-1 receptor ligands modulate gastrointestinal motility in mice

Cannabinoid-1 (CB1) receptors are broadly distributed in the central and peripheral nervous systems; among others, they are located in the enteric nervous system. In the gastrointestinal (GI) system, they participate in regulation of intestinal motility or ion transport. The aim of our study was to assess the effect of 1,2,3-triazole derivatives (compound 1: 2-[4,5-bis(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]-N-(2-fluorobenzyl)acetamide, compound 2: 2-[4,5-bis(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]-N-(4-fluorobenzyl)acetamide, compound 3: N-benzyl-2-[4-(4-chlorophenyl)-5-(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]acetamide]), characterized in vitro as CB1 antagonists with high CB1 over CB2 selectivity, in the mouse GI tract. The action of compounds 1-3 was assessed in vitro (electrical field stimulated smooth muscle contractility of the mouse ileum and colon) and in vivo (whole GI transit time). Compound 1 decreased ileal (10^-6 M) and colonic (10^-7-10^-6 M) smooth muscles contractility. Moreover, it prolonged whole GI transit. Compound 2 (10^-10-10^-8 M) slightly increased the amplitude of muscle contractions in the ileum, but at a higher concentration (10^-6 M), the amplitude was decreased. Compound 2 reduced colonic contractility but accelerated GI transit. Compound 3 decreased the amplitude of intestinal muscle contractions in the ileum (10^-6 M) and colon (10^-10-10^-6 M). Moreover, it increased the GI transit time in vivo. Triazole derivatives possess easily modifiable structure and interesting pharmacological action in the GI tract; further, alterations may enhance their efficacy at CB receptors and provide low side effect profile in clinical conditions.

Structure-Affinity Relationships and Structure-Kinetic Relationships of 1,2-Diarylimidazol-4-carboxamide Derivatives as Human Cannabinoid 1 Receptor Antagonists

We report on the synthesis and biological evaluation of a series of 1,2-diarylimidazol-4-carboxamide derivatives developed as CB₁ receptor antagonists. These were evaluated in a radioligand displacement binding assay, a [³⁵S]GTPγS binding assay, and in a competition association assay that enables the relatively fast kinetic screening of multiple compounds. The compounds show high affinities and a diverse range of kinetic profiles at the CB₁ receptor and their structure–kinetic relationships (SKRs) were established. Using the recently resolved hCB₁ receptor crystal structures, we also performed a modeling study that sheds light on the crucial interactions for both the affinity and dissociation kinetics of this family of ligands. We provide evidence that, next to affinity, additional knowledge of binding kinetics is useful for selecting new hCB₁ receptor antagonists in the early phases of drug discovery.

Blockade of Nicotine and Cannabinoid Reinforcement and Relapse by a Cannabinoid CB1-Receptor Neutral Antagonist AM4113 and Inverse Agonist Rimonabant in Squirrel Monkeys

Nicotine, the main psychoactive component of tobacco, and (-)-Δ(9)-tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, play major roles in tobacco and marijuana dependence as reinforcers of drug-seeking and drug-taking behavior. Drugs that act as inverse agonists of cannabinoid CB1 receptors in the brain can attenuate the rewarding and abuse-related effects of nicotine and THC, but their clinical use is hindered by potentially serious side effects. The recently developed CB1-receptor neutral antagonists may provide an alternative therapeutic approach to nicotine and cannabinoid dependence. Here we compare attenuation of nicotine and THC reinforcement and reinstatement in squirrel monkeys by the CB1-receptor inverse agonist rimonabant and by the recently developed CB1-receptor neutral antagonist AM4113. Both rimonabant and AM4113 reduced two effects of nicotine and THC that play major roles in tobacco and marijuana dependence: (1) maintenance of high rates of drug-taking behavior, and (2) priming- or cue-induced reinstatement of drug-seeking behavior in abstinent subjects (models of relapse). In contrast, neither rimonabant nor AM4113 modified cocaine-reinforced or food-reinforced operant behavior under similar experimental conditions. However, both rimonabant and AM4113 reduced cue-induced reinstatement in monkeys trained to self-administer cocaine, suggesting the involvement of a common cannabinoid-mediated mechanism in the cue-induced reinstatement for different drugs of abuse. These findings point to CB1-receptor neutral antagonists as a new class of medications for treatment of both tobacco dependence and cannabis dependence.

Central administrations of hemopressin and related peptides inhibit gastrointestinal motility in mice

BACKGROUND

Hemopressin was identified as an endogenous inverse agonist/antagonist of CB1 receptor, whereas VD-hemopressin(α) [VD-Hpα] and VD-hemopressin(β) [VD-Hpβ] were found as the novel endogenous peptidic agonists of cannabinoid receptors. As cannabinoids are potent modulators of gastrointestinal (GI) motility, our aim was to characterize the effects of hemopressin and related peptides on GI motility in vivo.

METHODS

The responses of intracerebroventricular (i.c.v.) administration of the reference compound WIN55,212-2, hemopressin, and related peptides to GI motility were investigated by measuring upper GI transit, colonic bead expulsion, and whole gut transit in mice.

KEY RESULTS

Central administration of the classical cannabinoid receptor agonist WIN55,212-2 dose-dependently slowed upper GI transit, colonic expulsion, and whole gut transit via CB1 receptor. Similarly, Hpα, VD-Hpα, and VD-Hpβ delayed upper GI transit and colonic expulsion after i.c.v. administration. At the high doses, Hpα and VD-Hpβ inhibited whole gut transit, whereas VD-Hpα had no effect on whole gut transit. In addition, the effects of these three peptides on GI transit were antagonized by the CB1 receptor selective antagonist AM251, but not by the CB2 receptor selective antagonist AM630.

CONCLUSION & INFERENCES

The endogenous cannabinoid peptide ligands hemopressin, VD-Hpα, and VD-Hpβ inhibited GI transit through the activation of CB1 , but not CB2 cannabinoid receptors. The lower potencies of the hemopressin and related peptides in GI transit assays may be important for the future development of cannabinoid peptides as the therapeutic analgesics with limited GI side effects.

X-ray analysis of gastrointestinal motility in conscious mice. Effects of morphine and comparison with rats

BACKGROUND

Non-invasive methods to study gastrointestinal (GI) motility are of high interest, particularly in chronic studies. Amongst these, radiographic techniques after contrast intragastric administration may offer many advantages. In previous studies, we have successfully and reproducibly applied these techniques together with a semiquantitative analysis method to characterize the effect of different drugs, acutely or repeatedly administered in rat models, but we have never before used these techniques in mice. These are very convenient in basic research. Our aim was to determine if our method is also valid in mice. Additionally, we determined the effect of morphine on GI motor function in both species.

METHODS

Animals received an intraperitoneal administration of morphine (at 10 and 5 mg/kg for rats and mice, respectively). Twenty min later, barium contrast (at 2 g/mL) was gavaged (2.5 and 0.4 mL for rats and mice respectively) and serial X-rays were obtained 0-8 h after contrast. X-rays were analyzed as previously described, using a semiquantitative score to build motility curves for each GI region.

KEY RESULTS

Motility was much faster in mice than in rats for all GI regions. Morphine at the doses used significantly depressed motility in both species to a similar extent if the whole gut or the upper GI regions (stomach, small intestine) were considered, although its effect seemed to be more intense in the lower GI regions (caecum, colorectum) in rats than in mice.

CONCLUSIONS & INFERENCES

We have validated our X-rays method for its use in mice.

The Endocannabinoid System and Its Role in Regulating the Intrinsic Neural Circuitry of the Gastrointestinal Tract

Endocannabinoids are important neuromodulators in the central nervous system. They regulate central transmission through pre- and postsynaptic actions on neurons and indirectly through effects on glial cells. Cannabinoids (CBs) also regulate neurotransmission in the enteric nervous system (ENS) of the gastrointestinal (GI) tract. The ENS consists of intrinsic primary afferent neurons, interneurons, and motor neurons arranged in two ganglionated plexuses which control all the functions of the gut. Increasing evidence suggests that endocannabinoids are potent neuromodulators in the ENS. In this review, we will highlight key observations on the localization of CB receptors and molecules involved in the synthesis and degradation of endocannabinoids in the ENS. We will discuss endocannabinoid signaling mechanisms, endocannabinoid tone and concepts of CB receptor metaplasticity in the ENS. We will also touch on some examples of enteric neural signaling in relation neuromuscular, secretomotor, and enteroendocrine transmission in the ENS. Finally, we will briefly discuss some key future directions.

Cannabinoid-based drugs targeting CB1 and TRPV1, the sympathetic nervous system, and arthritis

Chronic inflammation in rheumatoid arthritis (RA) is accompanied by activation of the sympathetic nervous system, which can support the immune system to perpetuate inflammation. Several animal models of arthritis already demonstrated a profound influence of adrenergic signaling on the course of RA. Peripheral norepinephrine release from sympathetic terminals is controlled by cannabinoid receptor type 1 (CB1), which is activated by two major endocannabinoids (ECs), arachidonylethanolamine (anandamide) and 2-arachidonylglycerol. These ECs also modulate function of transient receptor potential channels (TRPs) located on sensory nerve fibers, which are abundant in arthritic synovial tissue. TRPs not only induce the sensation of pain but also support inflammation via secretion of pro-inflammatory neuropeptides. In addition, many cell types in synovial tissue express CB1 and TRPs. In this review, we focus on CB1 and transient receptor potential vanilloid 1 (TRPV1)-mediated effects on RA since most anti-inflammatory mechanisms induced by cannabinoids are attributed to cannabinoid receptor type 2 (CB2) activation. We demonstrate how CB1 agonism or antagonism can modulate arthritic disease. The concept of functional antagonism with continuous CB1 activation is discussed. Since fatty acid amide hydrolase (FAAH) is a major EC-degrading enzyme, the therapeutic possibility of FAAH inhibition is studied. Finally, the therapeutic potential of ECs is examined since they interact with cannabinoid receptors and TRPs but do not produce central side effects.

Cannabinoids regulate intestinal motor function and electrophysiological activity of myocytes in rodents

BACKGROUND AND AIMS

This study aims to investigate the effects of cannabinoid (CB)1 and CB2 receptor ligands on intestinal motor function and muscular electrophysiological activity in rodent gastrointestinal (GI) tract.

METHODS

Lipopolysaccharide (LPS) was used to induce intestinal hypomotility. The effect of selective CB1 and CB2 agonists and antagonists on contractility of the muscle strips from rat jejunum was measured using organ bath, and the membrane potential of the jejunal smooth muscle cells was recorded with intracellular microelectrodes. The single cell patch clamp technique was applied to record delayed rectifying potassium currents (IKV) and spontaneous transient outward currents (STOC).

RESULTS

LPS significantly reduced contractility of the smooth muscle strips (p <0.010) and caused hyperpolarization of membrane potential of the smooth muscle cells (p <0.010). This LPS-induced effect was reversed by AM251 and AM630, selective CB1 and CB2 antagonists, respectively, which promoted contractions of smooth muscle strips and triggered cell depolarization (p <0.010). LPS-induced changes were further enhanced in the presence of CB agonists, HU210 and WIN55 (p <0.050 or p <0.010). No effect of HU210 or AM251 on IKV and STOC has been observed. This ex vivo study suggests that CB1 and CB2 receptors are involved in intestinal motor function in normal and LPS-induced pathological states and the regulation of the membrane potential of smooth muscle cells is very likely one of the effective mechanisms.

CONCLUSIONS

This is one of the first reports on neuronal regulation of intestinal motility through CB-dependent pathways with potential application in the treatment of inflammatory and functional GI disorders.

Inhibiting endocannabinoid biosynthesis: a novel approach to the treatment of constipation

BACKGROUND AND PURPOSE

Endocannabinoids are a family of lipid mediators involved in the regulation of gastrointestinal (GI) motility. The expression, localization and function of their biosynthetic enzymes in the GI tract are not well understood. Here, we examined the expression, localization and function of the enzyme diacylglycerol lipase-α (DAGLα), which is involved in biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG).

EXPERIMENTAL APPROACH

Cannabinoid CB1 receptor-deficient, wild-type control and C3H/HeJ mice, a genetically constipated strain, were used. The distribution of DAGLα in the enteric nervous system was examined by immunohistochemistry. Effects of the DAGL inhibitors, orlistat and OMDM-188 on pharmacologically induced GI hypomotility were assessed by measuring intestinal contractility in vitro and whole gut transit or faecal output in vivo. Endocannabinoid levels were measured by mass spectrometry.

KEY RESULTS

DAGLα was expressed throughout the GI tract. In the intestine, unlike DAGLβ, DAGLα immunoreactivity was prominently expressed in the enteric nervous system. In the myenteric plexus, it was colocalized with the vesicular acetylcholine transporter in cholinergic nerves. In normal mice, inhibiting DAGL reversed both pharmacologically reduced intestinal contractility and pharmacologically prolonged whole gut transit. Moreover, inhibiting DAGL normalized faecal output in constipated C3H/HeJ mice. In colons incubated with scopolamine, 2-AG was elevated while inhibiting DAGL normalized 2-AG levels.

CONCLUSIONS AND IMPLICATIONS

DAGLα was expressed in the enteric nervous system of mice and its inhibition reversed slowed GI motility, intestinal contractility and constipation through 2-AG and CB1 receptor-mediated mechanisms. Our data suggest that DAGLα inhibitors may be promising candidates for the treatment of constipation.

AM841, a covalent cannabinoid ligand, powerfully slows gastrointestinal motility in normal and stressed mice in a peripherally restricted manner

BACKGROUND AND PURPOSE

Cannabinoid (CB) ligands have been demonstrated to have utility as novel therapeutic agents for the treatment of pain, metabolic conditions and gastrointestinal (GI) disorders. However, many of these ligands are centrally active, which limits their usefulness. Here, we examine a unique novel covalent CB receptor ligand, AM841, to assess its potential for use in physiological and pathophysiological in vivo studies.

EXPERIMENTAL APPROACH

The covalent nature of AM841 was determined in vitro using electrophysiological and receptor internalization studies on isolated cultured hippocampal neurons. Mouse models were used for behavioural analysis of analgesia, hypothermia and hypolocomotion. The motility of the small and large intestine was assessed in vivo under normal conditions and after acute stress. The brain penetration of AM841 was also determined.

KEY RESULTS

AM841 behaved as an irreversible CB1 receptor agonist in vitro. AM841 potently reduced GI motility through an action on CB1 receptors in the small and large intestine under physiological conditions. AM841 was even more potent under conditions of acute stress and was shown to normalize accelerated GI motility under these conditions. This compound behaved as a peripherally restricted ligand, showing very little brain penetration and no characteristic centrally mediated CB1 receptor-mediated effects (analgesia, hypothermia or hypolocomotion).

CONCLUSIONS AND IMPLICATIONS

AM841, a novel peripherally restricted covalent CB1 receptor ligand that was shown to be remarkably potent, represents a new class of potential therapeutic agents for the treatment of functional GI disorders.

Bead study: a novel method to measure gastrointestinal transit in mice

BACKGROUND

Intestinal transit assessment in mice using existing methods requires long recording periods or euthanization of animals to localize a tracer. We have developed a novel in vivo method to assess gastrointestinal (GI) transit in mice based on a clinically used 'shapes study'.

METHODS

Mice (n = 70) were gavaged with 5 steel beads and barium 3 h before, with another dose of barium gavaged 10 min before imaging. Mice were fluoroscoped for 20-60 s, and then most of them were euthanized and the GI tract removed to confirm the localization of the beads fluoroscopically. The in vivo and postmortem recordings were analyzed and each bead was scored depending on its location; a total score was calculated by adding individual bead scores. Total scores obtained from the two methods were compared. A group of mice (n = 10) were examined on three occasions, before and after treatment with loperamide or prucalopride.

KEY RESULTS

The stomach and cecum were consistently outlined by barium, serving as reference landmarks. There was an excellent overall correlation between in vivo and postmortem transit scores (r = 0.93). Analysis of scores for individual gut segments revealed high agreement for stomach, cecum, and expelled beads, and moderate agreement for the small bowel and colon. Gastrointestinal transit scores were decreased by loperamide and increased by prucalopride compared with baseline.

CONCLUSIONS & INFERENCES

Metallic beads are reliably localized by videofluoroscopy in vivo within the GI tract. This novel imaging method enables repetitive measurements of GI transit in vivo and detects changes induced by motility-modifying agents.

2012 Division of medicinal chemistry award address. Trekking the cannabinoid road: a personal perspective

My involvement with the field of cannabinoids spans close to 3 decades and covers a major part of my scientific career. It also reflects the robust progress in this initially largely unexplored area of biology. During this period of time, I have witnessed the growth of modern cannabinoid biology, starting from the discovery of its two receptors and followed by the characterization of its endogenous ligands and the identification of the enzyme systems involved in their biosynthesis and biotransformation. I was fortunate enough to start at the beginning of this new era and participate in a number of the new discoveries. It has been a very exciting journey. With coverage of some key aspects of my work during this period of "modern cannabinoid research," this Award Address, in part historical, intends to give an account of how the field grew, the key discoveries, and the most promising directions for the future.

A role for O-1602 and G protein-coupled receptor GPR55 in the control of colonic motility in mice

Objective

The G protein-coupled receptor 55 (GPR55) is a novel cannabinoid (CB) receptor, whose role in the gastrointestinal (GI) tract remains unknown. Here we studied the significance of GPR55 in the regulation of GI motility.

Design

GPR55 mRNA and protein expression were measured by RT-PCR and immunohistochemistry. The effects of the GPR55 agonist O-1602 and a selective antagonist cannabidiol (CBD) were studied in vitro and in vivo and compared to a non-selective cannabinoid receptor agonist WIN55,212-2. CB_1/2^−/− and GPR55^−/− mice were employed to identify the receptors involved.

Results

GPR55 was localized on myenteric neurons in mouse and human colon. O-1602 concentration-dependently reduced evoked contractions in muscle strips from the colon (∼60%) and weakly (∼25%) from the ileum. These effects were reversed by CBD, but not by CB₁ or CB₂ receptor antagonists. I.p. and i.c.v. injections of O-1602 slowed whole gut transit and colonic bead expulsion; these effects were absent in GPR55^−/− mice. WIN55,212-2 slowed whole gut transit effects, which were counteracted in the presence of a CB1 antagonist AM251. WIN55,212-2, but not O-1602 delayed gastric emptying and small intestinal transit. Locomotion, as a marker for central sedation, was reduced following WIN55,212-2, but not O-1602 treatment.

Conclusion

GPR55 is strongly expressed on myenteric neurons of the colon and it is selectively involved in the regulation of colonic motility. Since activation of GPR55 receptors is not associated with central sedation, the GPR55 receptor may serve as a future target for the treatment of colonic motility disorders.

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G protein-coupled receptor 55 (GPR55) is a binding site for cannabinoids.

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No conclusive information was available on function of GPR55 in the GI tract.

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We found that targeting GPR55 at peripheral or central sites slows GI motility.

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Slowing effect of GPR55 activation on GI motility is primarily observed in colon.

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Targeting GPR55 may be a future tool for treatment of colonic motility disorders.

A potential role for GPR55 in gastrointestinal functions

Despite sharing little homology (10–15%) with cannabinoid-1 (CB₁) and cannabinoid-2 (CB₂) receptors, the G protein-coupled receptor 55 (GPR55) was initially thought to be a new member of the cannabinoid receptor family. Apart from being activated by various exogenous cannabinoids, GPR55 is also activated by endocannabinoids like anandamide, which is found in organs with high GPR55 expression such as the brain and the gastrointestinal (GI) tract. The phylogenetic distance to the classical CB receptors and its pharmacological responsiveness to certain cannabinoids suggests that GPR55 may constitute a novel class of cannabinoid receptors. GPR55 influences mechanisms in the nervous system, vasculature, kidney and bone. Recent research revealed that GPR55 is also involved in cancer development and inflammatory pain. Because of its presence in the GI tract, several studies have started to focus on the involvement of GPR55 in the physiology and pathophysiology of the gut. The following article intends to discuss the potential role of GPR55 in GI functions.

Inhibitory effect of cannabichromene, a major non-psychotropic cannabinoid extracted from Cannabis sativa, on inflammation-induced hypermotility in mice

BACKGROUND AND PURPOSE

Cannabichromene (CBC) is a major non-psychotropic phytocannabinoid that inhibits endocannabinoid inactivation and activates the transient receptor potential ankyrin-1 (TRPA1). Both endocannabinoids and TRPA1 may modulate gastrointestinal motility. Here, we investigated the effect of CBC on mouse intestinal motility in physiological and pathological states.

EXPERIMENTAL APPROACH

Inflammation was induced in the mouse small intestine by croton oil. Endocannabinoid (anandamide and 2-arachidonoyl glycerol), palmitoylethanolamide and oleoylethanolamide levels were measured by liquid chromatography-mass spectrometry; TRPA1 and cannabinoid receptors were analysed by quantitative RT-PCR; upper gastrointestinal transit, colonic propulsion and whole gut transit were evaluated in vivo; contractility was evaluated in vitro by stimulating the isolated ileum, in an organ bath, with ACh or electrical field stimulation (EFS).

KEY RESULTS

Croton oil administration was associated with decreased levels of anandamide (but not 2-arachidonoyl glycerol) and palmitoylethanolamide, up-regulation of TRPA1 and CB₁ receptors and down-regulation of CB₂ receptors. Ex vivo CBC did not change endocannabinoid levels, but it altered the mRNA expression of TRPA1 and cannabinoid receptors. In vivo, CBC did not affect motility in control mice, but normalized croton oil-induced hypermotility. In vitro, CBC reduced preferentially EFS- versus ACh-induced contractions. Both in vitro and in vivo, the inhibitory effect of CBC was not modified by cannabinoid or TRPA1 receptor antagonists.

CONCLUSION AND IMPLICATIONS

CBC selectively reduces inflammation-induced hypermotility in vivo in a manner that is not dependent on cannabinoid receptors or TRPA1.

Gut microbial products regulate murine gastrointestinal motility via Toll-like receptor 4 signaling

BACKGROUND & AIMS

Altered gastrointestinal motility is associated with significant morbidity and health care costs. Toll-like receptors (TLR) regulate intestinal homeostasis. We examined the roles of TLR4 signaling in survival of enteric neurons and gastrointestinal motility.

METHODS

We assessed changes in intestinal motility by assessing stool frequency, bead expulsion, and isometric muscle recordings of colonic longitudinal muscle strips from mice that do not express TLR4 (Tlr4(Lps-d) or TLR4(-/-)) or Myd88 (Myd88(-/-)), in wild-type germ-free mice or wild-type mice depleted of the microbiota, and in mice with neural crest-specific deletion of Myd88 (Wnt1Cre(+/-)/Myd88(fl/fl)). We studied the effects of the TLR4 agonist lipopolysaccharide (LPS) on survival of cultured, immortalized fetal enteric neurons and enteric neuronal cells isolated from wild-type and Tlr4(Lps-d) mice at embryonic day 13.5.

RESULTS

There was a significant delay in gastrointestinal motility and reduced numbers of nitrergic neurons in TLR4(Lps-d), TLR4(-/-), and Myd88(-/-) mice compared with wild-type mice. A similar phenotype was observed in germ-free mice, mice depleted of intestinal microbiota, and Wnt1Cre(+/-)/Myd88(fl/fl) mice. Incubation of enteric neuronal cells with LPS led to activation of the transcription factor nuclear factor (NF)-κB and increased cell survival.

CONCLUSIONS

Interactions between enteric neurons and microbes increases neuron survival and gastrointestinal motility in mice. LPS activation of TLR4 and NF-κB appears to promote survival of enteric neurons. Factors that regulate TLR4 signaling in neurons might be developed to alter gastrointestinal motility.

Endogenous cellular prion protein regulates contractility of the mouse ileum

BACKGROUND

Cellular prion protein (PrP(C) ) is expressed in the enteric nervous system (ENS), however, its physiological role has not been identified. Studies suggest that PrP(C) can function as a metal-binding protein, as absence of the protein has been linked to altered copper metabolism and atypical synaptic activity. Because copper is known to modulate smooth muscle relaxation, we tested the hypothesis that PrP(C) deficiency would alter intestinal contractility.

METHODS

We examined electrically evoked ileal contractility in Prnp(-/-) or wild type littermate mice and the effects of copper or copper chelation. PrP(C) expression was studied in whole mount ileal preparations of mice and guinea pigs by immunohistochemistry.

KEY RESULTS

Relative to wild type mice, ileal tissues of Prnp(-/-) mice exhibited reduced electrical field stimulation (EFS)-evoked contractility. Furthermore, EFS-induced relaxation, as a percentage of that induced by a nitric oxide donor, was enhanced. Addition of a copper donor to the organ bath increased, whereas the addition of a copper chelator inhibited, nitric oxide donor-induced ileal relaxation in Prnp(-/-) mice. PrP(C) was expressed on nerve fibers or terminals, and some cell bodies in the myenteric and submucosal plexuses of wild type mice. PrP(C) colocalized with a neuron-specific ectonucleotidase, nucleoside triphosphate diphosphohydrolase 3 (NTPDase3), but to only a limited extent with GFAP, a marker of enteric glia. Guinea pigs expressed PrP(C) in nerve fibers or terminals and enteric glia in the myenteric and submucosal plexuses.

CONCLUSIONS & INFERENCES

Our findings suggest that PrP(C) , which is abundant in the ENS, has a role in the regulation of ileal contractility.

The endocannabinoid system in inflammatory bowel diseases: from pathophysiology to therapeutic opportunity

Crohn's disease and ulcerative colitis are two major forms of inflammatory bowel diseases (IBD), which are chronic inflammatory disorders of the gastrointestinal tract. These pathologies are currently under investigation to both unravel their etiology and find novel treatments. Anandamide and 2-arachidonoylglycerol are endogenous bioactive lipids that bind to and activate the cannabinoid receptors, and together with the enzymes responsible for their biosynthesis and degradation [fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL)] constitute the endocannabinoid system (ECS). The ECS is implicated in gut homeostasis, modulating gastrointestinal motility, visceral sensation, and inflammation, as well as being recently implicated in IBD pathogenesis. Numerous subsequent studies investigating the effects of cannabinoid agonists and endocannabinoid degradation inhibitors in rodent models of IBD have identified a potential therapeutic role for the ECS.

Randomized pharmacodynamic and pharmacogenetic trial of dronabinol effects on colon transit in irritable bowel syndrome-diarrhea

BACKGROUND

Genetic variation in endocannabinoid metabolism is associated with colonic transit in irritable bowel syndrome (IBS) with diarrhea (IBS-D). The nonselective cannabinoid (CB) receptor agonist, dronabinol (DRO), reduced fasting colonic motility in nonconstipated IBS. FAAH and CNR1 variants influenced DRO's effects on colonic motility. Our aims were: (i) to compare dose-related effects of DRO to placebo (PLA) on gut transit in IBS-D, and (ii) to examine influence of genetic variations in CB mechanisms on DRO’s transit effects.

METHODS

Thirty-six IBS-D volunteers were randomized (double-blind, concealed allocation) to twice per day PLA (n = 13), DRO 2.5 mg (n = 10), or DRO 5 mg (n = 13) for 2 days. We assessed gastric, small bowel, and colonic transit by validated radioscintigraphy and genotyped the single nucleotide polymorphisms CNR1 rs806378 and FAAH rs324420. Data analysis utilized a dominant genetic model.

KEY RESULTS

Overall treatment effects of DRO on gastric, small bowel, or colonic transit were not detected. CNR1 rs806378 CT/TT was associated with a modest delay in colonic transit at 24 h compared with CC (P = 0.13 for differential treatment effects on postminus pretreatment changes in colonic transit by genotype). No significant interaction of treatment with FAAH rs324420 was detected.

CONCLUSIONS & INFERENCES

Overall, DRO 2.5 or 5 mg twice per day for 2 days had no effect on gut transit in IBS-D. There appears to be a treatment-by-genotype effect, whereby DRO preferentially delays colonic transit in those with the CNR1 rs806378 CT/TT genotypes. Further study of CB pharmacogenetics may help identify a subset of IBS-D patients most likely to benefit from CB agonist therapy.

Cannabinoid-induced delayed gastric emptying is selectively increased upon intermittent administration in the rat: role of CB1 receptors

BACKGROUND

Cannabinoids acutely administered depress central, cardiovascular and gastrointestinal functions. These effects might be modified upon repeated administration. Compared to the effects induced by daily administration, those induced by intermittent administration are less known. The effect of intermittent treatment with the CB1/CB2 cannabinoid agonist WIN55,212-2 (WIN) was studied in the rat.

METHODS

Male rats received saline, vehicle or WIN at 0.5 (low-WIN) or 5 (high-WIN) mg kg(-1) week(-1) for 4 weeks. WIN effects on the central nervous system (cannabinoid tetrad tests), cardiovascular function and gastrointestinal motor function were evaluated after the first and last doses, and, where appropriate, 1 week after the last dose. To determine the involvement of CB1 receptors in the chronic effect of WIN, the CB1 receptor antagonist/inverse agonist AM251 (1 mg kg(-1)) was used.

KEY RESULTS

High- (but not low-) WIN induced the four signs of the cannabinoid tetrad, and reduced gastrointestinal motility, but did not alter cardiovascular parameters. Upon chronic intermittent administration, tolerance did not clearly develop to WIN effects. Quite the opposite, depression of gastric emptying was intensified. No effect was long-lasting. Repeated administration of AM251 was more efficacious than single administration to block WIN chronic central effects, but the opposite occurred regarding lower intestinal motility.

CONCLUSIONS & INFERENCES

Upon intermittent administration, hypersensitization may develop to some effects (particularly delayed gastric emptying) induced by cannabinoid agonists. CB1 antagonists/inverse agonists may show different efficacy upon repeated or single administration to block cannabinoid-induced central and gastrointestinal effects. Thus, cannabinoid effects are dependent on the pattern of drug administration.

Gut feelings about the endocannabinoid system

Stemming from the centuries-old and well known effects of Cannabis on intestinal motility and secretion, research on the role of the endocannabinoid system in gut function and dysfunction has received ever increasing attention since the discovery of the cannabinoid receptors and their endogenous ligands, the endocannabinoids. In this article, some of the most recent developments in this field are discussed, with particular emphasis on new data, most of which are published in Neurogastroenterology & Motility, on the potential tonic endocannabinoid control of intestinal motility, the function of cannabinoid type-1 (CB1) receptors in gastric function, visceral pain, inflammation and sepsis, the emerging role of cannabinoid type-2 (CB2) receptors in the gut, and the pharmacology of endocannabinoid-related molecules and plant cannabinoids not necessarily acting via cannabinoid CB1 and CB2 receptors. These novel data highlight the multi-faceted aspects of endocannabinoid function in the GI tract, support the feasibility of the future therapeutic exploitation of this signaling system for the treatment of GI disorders, and leave space for some intriguing new hypotheses on the role of endocannabinoids in the gut.